Method of welding



Nov. 26, 1.940. c. G. JONES METHOD OF WELDING Filed Oct. 18, 1938 5 Sheets-Sheet 2 Nov. Z6, 1940. C G JQNES 2,222,977

METHOD OF WELDING INVENTOR Car/ G, Jones Nov. 26, 1940. c. G. JONES METHOD OF WELDING 3 Sheets-Sheet 3 Filed Oct. 18, 195B INVENTOR Carl G Jones Patented Nov. 26, 1940 UNITED sTATizs METHOD 0F WELDING Carl G. Jones, Youngstown, Ohio, assignor to The Youngstown Sheet & Tube Company, Youngstown Ohio, a corporation of Ohio Application october 1s, 193s, serial No. 235,569

5 Claims.

This invention relates to electric welding and, particularly, to what I shall herein designate as arc-resistance welding.

Various forms of electric welding are now known and have been successfully practiced for many years. In resistance welding, the passage of electric current between abutting metallic surfaces causes heating at the spaced points at which the surfaces are in contact. The high points of the surfaces, on continued heating, are gradually burned away and the entire surface is heated to such an extent that a weld can be effected.

The high points iirst make contact and are iused back to the edges. From these fused points the heat spreads to the adjacent portions of the edges until the whole edge suriace is heated to a fusing or welding temperature. From this point the temperature continues to increase until the high specific resistance due to high temperature reduces the current flow.'

If the voltage applied across abutting metallic surfaces is raised above a predetermined minimum value, the heating of the surfaces proceeds more rapidly and the contacting portions thereof are actually volatilized and ejected with considerable force. The rather violent evolution of volatilized material instantaneously exposes portions of the metal surfaces to atmospheric oxidation. This leaves brittle spots in the weld when nished because of the resulting thin oxide layer prevents perfect union of metal to metal, producing a discontinuous weld.

The usual arc weld between adjacent metal surfaces is made by feeding the members to be welded toward each other at the rate at which the opposed surfaces are burned off or volatilized by the arc, thus progressively to heat up portions ofthe metal spaced from the extreme edges whereupon they may be forced together and welded. Both arc weldingand resistance welding as now practiced are made possible by allowing suiiicient time to burn'off, ory upset the `opposed edges. tothe extentpat least, of the thickness of the piece beingrwelded, and byv insuring intimate contactaV kOtherwise expressed,y the conditions for satisfactory weldingby either the yarc or resistance methodare suiiicient'time and accurate kvcontrol of conditions.V l

It has been attempted'heretofore to utilize both arc welding'an'dresistance welding by a combi-r nation 'of the'l two methods which I shalll designate herein as'arc-resistance welding.l `An example of this practice is the induction Welding (ci. 21a-1o) of pipe from cylindrical blanks each having a longitudinal seam cleft defined by the edges of the flat skelp from which the blanks are formed. According to the method previously practiced, the blanks were subjected progressively to the action of a periodically varying magnetic field of such character as to induce currents flowing circumferentially thereof and across the seam cleft. The seam cleft was progressively closed as the heating of the edges thereof proceeded and a continuous weld finally effected. In this method of welding, the heating is the result of the arcing between the edges of the seat cleft prior to the initial contact thereof as well as of the resistance of the joint after the initial contact. The circumferentially induced' currents have a metallic path from the point of initial contact of the seam cleft edges onward to the end of the ,zone of inuence of the magnetic field. In the other direction (i. e., that in which the seam cleft edges diverge) current flows across the seam cleft forming an arc, as far back along the cleft as the applied voltage is capable of forcing current across the widening cleft. 'I'he magnitude of this voltage is determined by the intensity of the magnetic field and is usually a. compromise between the optimum voltage for resistance Welding and the minimum voltage required for arc welding. There is obviously a substantial difference between these voltages, since, in resistance welding, the pipe constitutes substantially a short circuit.

Certain objections to the previous practice have been encountered in actual operations. In the first place, the induced voltage across the seam cleft, in order to provide stable arcing, must be too high for satisfactory resistance welding. In a particular case, for example, a voltage of about fifteen volts is preferred for arc welding. The voltage desired for resistance welding, however, is much lower, of the order of three to five volts. The result of excessive voltage in the resistance heating zone is a violent explosive action resulting in the formationl of the oxidized spots in the iinished Weld 'as previously described. If the welding zone is made fairly long, furthermore, to obtain good coupling betweenthe inducing coil usually employed to produce the magnetic iield, and the advancing pipe blank, the voltage across `the seam` cleft is' so high that too much metal is burned oir. If the welding speed is increasedto prevent excessive burn-oil?, the speed` of the. entering cold .edges is too great yfor a stable arc toform and as a tion of the length of the tube blank at each end y tensities to induce a vvoltage between opposed` thereof is left unwelded and must be cut oir and scrapped. ,v y

I have invented a novel method of arc-resistance welding which overcomes then aforementioned objections and is characterized'by further novel features and advantages. I pass the edges to be welded through a succession of independy ently controlled magnetic elds of vdifferent inpoints valong the edges of the seam cleft substantially above the minimum necessary to cause an arc between suchy points and then,- after preliminary heating by arc currents, 4to induce a voltage between said points substantially below saidminimum arcing value, yet sumcient to cause heavy circumferential currents to iiow across the Acleft after the edges have been r abutted, thus continuing theheating by the resistance method. After the edges of the cleft have been heated to welding temperature in this manner, they are pressed firmly together to complete the weld. Briefly stated, the invention comprises subjecting the edges for a dennite length of time to a voltage substantially above the minimum arcing value and then for a further time to a voltage substantially lower than said minimum to continue the heating bythe resistance method.

'Ihe apparatus which I prefer to employ in practicingl the invention comprises an inductor having separate `coils thereonA for inducing the arc heating voltage and the resistance heating voltage respectively. Independent control means for regulating the excitation of these coils makes it possible so to adjustthe intensities of -the magnetic elds produced thereby that the desired voltages' are induced in both the arcing heating zone andthe resistance heating zone. The invention will be described in detail hereinafter with reference to the accompanying drawings illustrating the practice and apparatus of my invention as applied to the example hereinbefore mentioned, viz., the welding of pipe from cylindrical blanks, but it is to be understood that the invention is also equally applicable to the welding of metal members of other forms.' In the drawings:

Fig. l'nis a longitudinal-vertical sectional view through a welding apparatus embodying `the invention;

Flg.2isasectionalviewshowing a Eig. i to enlarged scale;

Fig.3isapartialtransversesectionalview portion of taken along the line UI-III of Fig. 2;

Fig. 4 is a diagram showing'the electrical circuits for exciting and controlling the inducing coils; and ,ll'igisagraphshowingthevariationofthe vapplied voltage from Polntto point along the heatingsone.

Referringnowindetailtothedrawingsand, forthepreeent particularlytorlg.i.pipe welding apparatus embodying my invention is indicatedgenerallyatllandccmprisesat-pedo Il,astsndoffeedinrolls Ilandastandot weldingrolls Il. 'Ihestandsoffeed-inand welding rolls are of known construction so a detailed description thereof is not necessary. It should be stated, however, that the bottom roll I4 of the feed-in stand has a central nn I5 adapted to enter the seam cleft Il of an advancing pipe blank l1. to maintain the edges thereof in spaced relation. The torpedo Il comprises a tubular shell I8 disposed on any suitable frame work including a depending plate Il anchored to a supporting structure 20. .The advancing pipe blank thus embraces the torpedo preparatory to passing through the throats defined by the feed-in and welding rolls, the edges of the seam cleft passing on opposite sides of the plate I9.

A coil and core` assembly indicated generally at 2l is mounted on the torpedo by means of a tension rod 22 extending rearwardly and being attached to the torpedo frame: (The terms fforwardlyf and rearwardly as used herein apply to the direction of travel of the pipe blank indicated by the arrow 23.) The forward end of the torpedo is provided with supporting and guide rolls 24 adapted to travel along the interior of the pipe. Guides 25 and shoes 25 mounted in any convenient manner on the stands I2 and I3"cooperate to direct the blank emerging from the rolls of standy l2 into the rolls of stand Il.

The coil and core assembly 2|, hereinafter referred to as the inductor, is shown in detail in Figs. 2 and 3. The core is shown at 21. It is substantially cylindrical in shape and is composed of laminations assembled between supporting plates 2l. A layer of insulating material 2l surrounds the core. The plates 2l are connected at their ends by plates Il secured thereto, the tension rod 22 being secured to the rear--plate Il by gusset plates Il.

Inducing coils I2 and 33 are disposed on the core 21 in spaced relation. Adjacent turns of the coils are separated by spacing rings Il and adjacent layers by annular layers of insulation Il. Exciting current is supplied to the coils by means to be described shortly, the supply conductom extending from' the ecoils rearwardly through the to and radially along the plate Il to the exterior of the blank. An outer layer of insulation II surrounds the coils. Pole pieces I1 formed of annular laminations are disposed between each coil and the adjacent end of the core. A similar pole ,piece 3l is disposed between thecoils. The pole pieces I1 may conveniently be assembled between the end plates Il and annular spacer plates Il. The pole piece ID is similarly disposed between spacer plates Il.' The entire coil and core assembly may be protected by spacedarmorin'g plates ,Q I if desired but it is essential that no continuous conducting path beprovided circumferentially o! the inductor. except, of course, that provided by the blank I1. Acoolingiacketmaybeatt'achedtothe armoringplatenearesttheseambeingwelded inordertoprotecttheinductorfromtheheat thereof. Coolingwaterissuppliedtoandcollected from the Jacket by connections Il extending rearwardly along the torpedo and outward thereof in the same manner as the conductors ofthe circuit nipplyingexeitingcurrenttothe primary wlndingan and Il.

It will be understood from the foregoing descriptionthattheinductor andtheblank l1 constituteatransformentheblankbeingasecondary winding wherein currents v circulate.

throughthemialtrarutormeractiominoppoliu tion to the currents traversing the primary windings 32 and 33. To reduce the reluctance of the magnetic circuits, yokes 44 are disposed in spaced relation about the inductor. 'I'he shape of the yokes in side elevation is shown in Fig. 4, from which it will be seen that they have poles cooperating with the pole pieces 31 and 33. 'I'he yokes 44 are mounted on supporting members 45 (see Fig. 1) mounted for pivotal movement adjacent their upper ends, and an adjusting screw shaft 4B connects the upper ends of the supports 45 whereby they may be moved closer together or farther apart, thereby adjusting the spacing between the yokes 44 and the blank I1.

Fig. 4 illustrates one form of supply circuit and control means therefor. As there shown, a three phase supply circuit 41 extends to transformers 49 and 50 arranged in the so-called Scott connection to energize two single phase exciting circuits 5I and 52. The circuit 5I is connected to the coil 32 and the circuit 52 to the coil 33. Each circuit has a current control device illustrated as a rheostat 53. It will be understood, however, that any convenient type of control mechanism may be substituted therefor such as induction regulators, transformers or auto transformers with tap changing equipment, or a combination of these elements.

In the use of 'the apparatus described to perform the method of my invention, a formed pipe blank such as that shown at I1 is advanced over the torpedo II with its seam cleft in alignment with the supporting plate I9 and the i'ln I5 on the bottom roll I# of the feed-in stand I2. Any suitable means (not shown) may be employed for advancing the blank to a position in which its leading end enters the feed-in stand I2. The rolls of the stands I2 and I3 are driven by mechanism already known. The rolls of stand I2 operate as pinch rolls but because of the n on the bottom roll I4, the seam cleft I6 remains open until a. point between the stands I2 and I3 is reached.

As the leading end of the blank passes over the inductor, the flux produced by the coil 32 in the magnetic circuit indicated generally at 54 in Fig. 2 induces a Voltage circumferentially of the blank. Since the seam cleft is still open, however, no current flows across the cleft because the voltage is insufficient to break down the air gap between the cleft edges. The leading end of the blank then advances further until it comes into the zoneof influence of the coil 33, i. e., the magnetic circuit indicated at 55. As the end of the blank advances, the guides 25 and shoes 26 contract the blank forcing thzedgespf the cleft into abutment at a point about midway between the stands I2 and I3. At the first contact, current ilows between the cleft edges and an arc is formed immediately by the resulting heating, between the portions ofthe cleft edges kwhich have not `yet been Ybrought into contact; vOnceinitiated, the

arc extends rearwardly until the distance between* the cleft edges is greater than that across which the available'volt'age will cause a flow of current in the preser'ice` of the heat and ionized condition of the atmosphere created by the'v arcing between the edgesy at pointsl rearwardly from the point' at the spacing at which they are maintained at that point in their travel. For example, while a voltage of the order of 10 or 11 volts is about the minimum which will maintain an arc between the edges at the spacing at which they are maintained in the neighborhood of the coil 32, I excite the latter suiiiciently to induce a voltage of from 14 to 16 volts circumferentially of the blank. On the other hand, when the cleft edges have been brought into contact and are in the zone of inuence of the coil 33, I subject them to magnetic field of the proper intensity, determined by regulating the rheostat 53, to induce a circumferential voltage of from 3 to 5 volts.

The arc flushes the blank edges and leaves the extremities thereof in a' molten state so that they will adhere to each other on initial contact but not be welded to each other. The edges are progressively pressed together from the instant of first contact until they pass out of the weld stand I3, where they are firmly pressed together, and the weld completed.,

Fig. 5 illustrates roughly the voltages induced circumferentially of the blank at various points in its movement over the inductor. The left hand end of curve 56, for example, shows the voltage induced in the blank -at points in alinement therewith on Fig. 2. It will be noted thaty the voltage does not appear until the blank has reached substantially the mid-point of the coil 32 and the voltage decreases slightly with movement of the blank toward the welding stand.l As shown by the curve, the voltage varies between 16 and 14 volts which is substantially in excess of the minimum voltage (roughly'lO volts)Y indicated by ordinatega required to initiate an arc. For this reason, thev effect of the coil 32 is to produce and maintain a strong arc across the seam cleft capable of effecting rapid heating of the edges.

The effect of the coil 33 is to induce' acircumv ferential voltage iny the blank as illustrated by the right hand end of curve 56. Asillustrated", this voltage varies from about 6 kvolts to about 3 volts by the time the pointA on the'bl'ank has passed beyond the endv of the inductor.' This` voltage is suiicient to produce heavy circumferential currents for resistance heating butnot to 4cause the violent explosive action observed with previous welding methods and apparatus' 'in which the voltage for resistance heating was not very different from that employed for arc welding. f

Between the initial and finalv stages of heating by arc and resistance' is a transition stage` so marked on curve 56 during whichthe voltage circumferentially of the blank Yfalls sharg'ily. At

about the mid-point ofthis transition stage the n arc ceases and further heating is en'e'cted by resistance.

As the trailing end Iof the'blank'uncovers theT coil 32, -the arcing' voltage 'will'drop rapidly.

This drop in the voltage may be compensated" for by increasing the excitation of thecoil 32 or of thecoil 33. I preferto-dothefffornier. 'Ihe necessary regulation' of (the current'may' 'bef effected manually ory automatically by any suit'- able means, in accordance with lthe movementof the blank over the* inductor; 'f f vliigf also includes curve 51 which illustrates,

for the ymimosa of differentiation, the voltages *f circumferentially of a -pipe blank produced by a typical inductor of the form used heretofore. As in the case of curve 56, the ordinates represent the circumferential voltage and the abscissae the distance rearwardly from the axial plane of the rolls of the welding stand. It will be readily understood from Fig. 5 that the apparatus used heretofore was capable of initiating arc heating current only after the cleft edges had quite closely approached the point of actual contact and that the voltage available to produce arc heating current was sufiicient only to maintain a relatively feeble arc. On the other hand,

the voltage available to produce resistance heating beyond the point of actual contact of the edges was greatly in excess of the necessary voltageso that the violent explosive action heretofore mentioned was experienced.

It will be appreciated that the invention makes it possible for the iirst time to apply to the different stages of an arc-resistance heating operation, voltages appropriate to the character of heating and amount of current desired. By eliminating the violent explosive action heretofore encountered in the resistance heating stage, I avoid discontinuity in the weld resulting from oxidation spots'produced by such action. The invention also makes it possible to weld at greater speed than has been attained heretofore 'loss represented by the unwelded end portions` is reduced by the invention to about one-third of the amount previouslyveiperienced, at both leading and trailing ends. As stated, the,arc heating conditions the edges by burning oi! variations from true parallelism. The resistance heating, furthermore, may be individually controlled to obtain the desired character of heating, i.. e., either moderate or intense. The tapering throat formed by the guides 2l and 2l gradually increases the pressure between vthe edges to be welded, thus extruding all oxides or.

cold spots, i. e., spots not heated vto welding temperature.

A further advantage of distinct value is that since the resistance heating is marked by the absence oi' any violent explomve` action, there is no spray of burned of! metal to deposit on the welding rolls. This eliminates slag markings on the pipe and reduces the frequency oi the necessary periodical removal oi' slag deposited on the shoes. some flying hot metal, the amount thereof i8 considerably reduced by the invention and it is concentrated at a distance from the rolls of the stands I2 and I3. 'Ihe aforementioned extrusion oi' hot metal ha's the further advantage of preventing too rapid cooling of the welded seam and the brittleness of the weld which would otherwise result therefrom.

While I have illustrated and described herein but a preferred embodiment and practice of the invention, it will be understood that changes While the arek heating stage'produoes therein may be made Awithout departing from the spirit oi' the invention or the scope of the appended claims. As already stated, the application of the invention to pipel welding disclosed herein is purely illustrative and it is not to be considered as limited thereto.

Iclaim:

1. In a method of welding longitudinally moving metallic edges converging gradually into engagement with each other, the steps including progressively applying between said edges at points at which they are spaced apart, a voltage substantially higher than the minimum needed to. establish and maintain an arc between said edges, concurrently applying .progressively between said edges, at points at winch they have engaged, a -voltage substantially lowerthan said minimum, and when said edges have been heated to welding temperature, pressing them nrmly together.

2. The method as dened by claiml 1 characterized by applying said voltages by electromagnetic induction.

3. In a 'method of making pipe from substantially cylindrical Vblanks having a longitudinal seam cleft by moving the blank and gradually forcing the edges together, the steps including progressively applying between said edges at points at which they are spaced apart, a voltage substantially higher than the minimum needed to establish and maintain an arc between said edges, concurrently applying progressively between said edges, at points at which they have engaged, a voltage substantially lower than said minimum, and when said edges have been heated to welding temperature, pressing them iirmly l together.

I 4. In a method of making pipe from substantially, cylindrical blanks having a longitudinal seam cleft by moving the blank and gradually forcing the edges together, the steps including progressively applying between said edges at points at which they are spaced apart, a voltage substantially higher than the minimumvrequired to establish an arc between said edges, thereby creating an arc-heating zone, concurrently applying progressively between said edges, at points at which they have engaged, and at a predetermined distance from said zone, a voltage substantially lower than said minimum, thereby creating a resistance-heating zone and, when said edges have been heated to welding temperature, progressively pressing themiirmlytogether.

l5. In a method of making pipe from substantially cylindrical blanks having a longitudinal seam cleft by moving the blank and gradually forcing the edges together, the steps including vely applying between said edges at points at which'they are spaced apart, a voltage at least 40% higher than the minimum required to establish an arc between said edges, thereby creating an arc-heating sone, concurrently applying progressively between said edges, at points 

